1. Field of the Invention
The present invention relates to the construction for a bearing assembly for a jet pump upon which a boat or similar water-traveling vessel relies for propulsive power.
2. Description of the Related Art
A number of modern watercraft and sport boats rely entirely on jet propulsion technology, such as a jet propulsion drive system, to provide the propulsive force for the vessel.
A jet propulsion drive system (also called a jet pump drive) incorporates an impeller within a pump housing at a position toward the rear of the watercraft. The pump housing is disposed within a inlet duct that extends, at the bottom of the hull, from a point at the rear of the vessel to a point forward of the rear of the vessel. The impeller is operatively connected, through a rotatable shaft, to an engine typically disposed within the hull of the vessel. When rotated by the engine, the impeller draws water through the forward end of the inlet duct and discharges the water, at great speed and pressure, through a nozzle at the rear end (or stern) of the vessel. The force of the water exiting from the nozzle at the stern generates the propulsive force for the vessel.
The impeller is usually affixed to the pump housing through a stator or stator hub, which connects to the pump housing by three or more connecting vanes. The stator or stator hub is a fixed (i.e., non-rotating) element within the pump housing that surrounds the end of the rotatable shaft that extends beyond the rear end of the impeller.
To stabilize the end of the rotating shaft, the stator includes an interior support into which at least two bearings are usually inserted. The outer races of the bearings are affixed to the interior support of the stator and the inner races of the bearings are affixed to the rotatable shaft on which the impeller is disposed.
FIGS. 1-3 illustrate the first embodiment of a jet drive assembly known in the prior art. In this embodiment (as discussed in greater detail below), two roller bearings are disposed an axial distance from one another along the rotating shaft to freely support the rotation of the shaft.
FIG. 4 illustrates a second embodiment of a jet drive assembly known in the prior art. In this embodiment (also as discussed in greater detail below), two ball bearings are disposed an axial distance from one another along the rotating shaft to freely support the rotation of the shaft.
In either prior art jet drive assembly, grease (or other suitable lubricant such as oil) is usually added to the bearings after the jet pump is assembled and before the watercraft is delivered to the customer. Grease (or oil) lubricates the rollers and balls within the bearings to assure a more efficient and smooth operation.
A problem with the prior art, however, is that the rotating shaft, stator, and other associated components must be made sufficiently long to accommodate two bearings disposed a specific axial distance from one another.
In addition, prior art pump bearing assemblies tend to generate noise due to play (e.g., mechanical tolerances) incorporated therein as a result of the construction techniques employed. With the configuration(s) known in the prior art, the bearings tend to wear at a rate that, while acceptable, could be improved.
In addition, due to the tolerances incorporated into the bearings frequently used in the prior art, the watercraft often required an additional anti-rattle system to minimize the noise generated by the pump during operation.
Finally, the bearings in some prior art jet pump assemblies often require re-lubrication after a certain amount of time. In other words, the lubricant (e.g., grease or oil) in the bearings must be replaced or replenished after a certain time period. This is necessary primarily because the bearings in the prior art typically are not completely sealed. Accordingly, the lubrication incorporated into them often leaks out of the bearings over time.
Each of these deficiencies in the prior art, while they do not negatively impact upon the operational or safety characteristics of the watercraft in which the jet pump assembly is installed, ask for improvement.